Along with cheerful holiday greetings, the mail this month is bringing pictures of maimed veterans, gnarled lepers and destitute, sunken-eyed children.

It is all part of a billion-dollar, fund-raising effort timed by scores of sponsoring charities to peak during the holiday season when people are more likely to be influenced by such appeals and are often looking for year-end tax deductions.

Many of the appeals are low-keyed and straightforward, like the envelope-sized computer cards sent by the Salvation Army and the traditional Christmas seals from the American Lung Association.

Many offer sentimental meanderings, like the rendition of "The Little Drummer Boy" offered by the Cedars Home for Children. There are unsolicited rosaries, personalized address labels, plastic holy statues and appeals from celebrities, like former Redskin quarterback Sonny Jurgensen (Alexandria Hospital and singer Pat Boone, who sends out a shiny copper penny and a portrait of his family in an appeal for "Bibles for the (Communist) World."

Some consumers refer to this volume of paper and cheap plastic gimmicks as "junk mail." But fund raisers contend grumblers are in the minority. The direct-mail solicitation system, now honed to a science, is tailored to preferences of the majority of Americans who want to give, they say.

"There are a lot of lonesome people who like to hear from someone," said Andy Andrews, president of American Fund-raising Services, a Boston-based firm whose clients are medical, educational and cultural organizations.

In fact, the Direct Mail Marketing Association's mail preference service receives more requests from individuals wishing to be added to mail solicitation lists - including commercial catalogues, magazines and mail-order offers - than to be removed from lists.

Your name most likely has been bought, sold, traded or rented simply because you are listed in the telephone book, opened a credit card account or purchased a magazine subscription.

And the charities computers probably know more about you than you know about most of them. You may be classified on one list by your income status, another by your politics and still another because you are left-handed.

The content of the mail appeals has also been tested by the charities to determine which design is most productive financially.

"I don't like sending cards. It's like putting a knife to people's throats," said the Rev. Aloysius Schwartz, whose charity, Korean Relief, Inc., in Mount Rainer, Md., has enclosed five colorful Christmas cards in its holiday mailing.

"But you just can't do it without the fight," he contended. "We've tested and rested cards versus embroidered items, seals, a plain letter, and so on. People think we're idiots to flood the mails with this junk. If someone could give me another way to do it, I'd do it."

The Blinded Veterans Association has learned that the picture of "Bill," who is blind and maimed below both elbows, has been its most successful mail appeal.

"We're not trying to shock people, although I guess it does," acknowledged Summer Vale, acting executive director of the Washington-based agency. "We're trying to show that some of these blinded veterans have multiple handicaps and that rehabilitation, or becoming a useful and productive citizen, is the name of the game."

Added Vale: "We're obviously asking for help, but we do not want to project an oversympathetic approach."

In somewhat different vein, American Near East Refuge Aid appeal conjures painful images of war and homelessness. "I remember the scene of 1948, children screaming . . ." writes a "Palestinian refugee" in one letter. And from Arlington, the Missionhurst priests are circulating photos of smiling African children with a stern caveat. What would happen, the Rev. Louis Tysmans writes, if the boy pictured goes hungry and his "laughing brown eyes" turn "lifeless" and his teeth "begin to decay and fall out . . ."

And there's Bobbie Sue, who is starving in Appalachia.The Christian Appalachian Project has sent personalized address labels on behalf of Bobbie Sue, who they note receives no mail of her own. Her "Pa" is dead and her mother barely collects enough wages to feed her children.

Or for $2 or $3, a donor could help buy a window pane or for $50 purchase enough cement to stucco a house for Indians. One seven-member family, the "Manygoats," live in such a tiny ramshackle dwelling that the Rev. Douglas A. McNeil of the Southwest Indian Foundation wrote that he "had to be careful not to step on one of the children" on the dirt floor when he visited.

In fiscal 1977, nonprofit organizations sent out 6.5 billion pieces of bulk third-class mail, an increase of 10 per cent over the previous year, according to the U.S. Postal Service.

Americans contributed nearly $30billion to charities during the same period, up 9.4 per cent from 1976, the American Association of Fund-Raising Counsel, Inc., reported. Experts believe that three-fourths of donations result from direct mail appeals.

The Council of Better Business Bureau's Philanthropic Advisory Service in Washington has been receiving about 500 inquiries daily this month from individuals who "want to give" but are looking for the "right" charity, said director Helen O'Rourke.

One inquiry turned up information that the Christmas appeal of the Salesian Missions of New Rochelle, N.Y., was offering a sweep-stakes prize of a new 1978 Chevrolet Vega. The last model year for the Vega was 1977.

"It was a printing error," said a receptionist in teh Salesian Missions office. "We are now offering a 1978 Nova."

The Better Business Bureau also publishes a list of charitable organizations that do or do not meet its soliciation standards. The 207 "acceptable" groups provide financial disclosures, inform prospective donors that they are under no obligation to pay for unsolicited merchandise, and spend a "reasonable" percentage of their total income on charitable programs.

The cost for direct mail appeals can range roughly from 20 to 60 per cent of charitable revenues. Consequently most states have enacted laws regulating charitable solicitations, including some large-volume religious groups. In Maryland, for example, the ceiling on fund-raising costs is 25 per cent of the income, plus postage, and the rest is expected to be spent on the charitable project.